Amax Gold Inc. of Englewood, Colo., agreed yesterday to be acquired by the Kinross Gold Corporation of Toronto in a stock deal under which each Amax share will be exchanged for 0.8 Kinross share. Shares of Amax closed yesterday at $3.3125, up 12.5 cents, on the New York Stock Exchange. Kinross closed at $5.25 (Canadian), the equivalent of $3.66 (United States), on the Toronto Stock Exchange. With more than 114.8 million shares outstanding, Amax’s stock would be worth more than $420 million (United States). The merger will make Kinross the fifth-largest gold producer in North America, Amax said.